Since dynorphin A1-17 has been shown by previous studies to be presumably the major endogenous kappa ligand and its effects would be shared by both the shorter dynorphin A1-13 as well as the shorter and stabilized dynorphin A1-10 amide, we are conducting studies of the effects of these dynorphin A peptides in normal volunteer subjects both to determine the effect on hormones of the hypothalamic-pituitary-adrenal axis.